Further pharmacologically active alkaloids have been isolated from skin extracts of dendrobatid frogs. The structures and pharmacology of these compounds continues under investigation. The pumiliotoxin A class represents a series of potent myotonic and cardiotonic agents, for which tentative structures have been derived. An analgesic agent of as yet unknown structure appears to belong to this class of dendrobatid alkaloids. The compound inhibits binding of dihydromorphine to the opiate receptor in brain membranes. Histrinicotoxins bind to a macromolecule which appears to be associated in membrane but not in soluble preparations with the nicotinic acetylcholine receptor. It would appear that this macromolecule represents the ionic channel controlled by the acetylcholine receptor. An analog of batrachotoxin binds with high affinity to a regulatory site associated with the sodium channel in brain membranes. Compounds which inhibit the binding of ouabain to Na ion-K ion-ATPase in erythrocytes have been detected in skin extracts from not only bufonid toads but a number of other species of amphibians.